Flat panel displays are a future-oriented trend for the display industry. In particular, the liquid crystal display (LCD) attracts more attention thanks to its thin-profile, lightweight, lower radiation, lower power consumption and higher resolution and brightness. LCDs are now widely used in various applications from PCs, commercial display panels to home theaters.
The LCD is optimally suited for commercial display panels (rather than home theaters) thanks to its high brightness. This is owing to the fact that the brightness of an LCD is generated from backlit modules, which may change the light permeability by controlling the torsion of LCD, thus identifying the image brightness (gray level). If the images are displayed on an 8 bit LCD, the maximum brightness is observed at an image gray level of 255, or minimum brightness observed at image gray level of 0. At present, the brightness of an LCD TV is about 400 cd/m2˜600 cd/m2 at a gray level of 255, or 0.5 cd/m2˜1.4 cd/m2 at gray level of 0.
In order to adjust the quantity of light entering the human eyes, the pupil will zoom in/out, depending upon the strength of ambient light. When large-area high-gray level images (e.g. snow) are displayed on TV, the pupils of human eyes will zoom out to reduce the quantity of light entering the human eyes. When low-gray level night scenes are displayed in TV, the pupil will zoom in to increase the quantity of light entering the human eye. In practice, brightness or darkness of images varies alternatively, coupling with zoom in/out of pupil. Thus, a high-brightness LCD enables continuous zoom-in/out of a pupil, leading to easy fatigue of human eyes.
FIGS. 1 and 2 depict the relationship between brightness and brightness ratio of a CRT TV and an LCD TV. The optical flux of the TV is represented by the product of display ratio and brightness ratio. If the brightness ratio is observed to be more than a specified value, optical flux of the CRT TV is close to a steady state, so the variation of images will not lead to excess zoom-in/out of pupils and fatigue of eyes. To the contrary, optical flux of the LCD TV will vary markedly with the brightness ratio. If the images often vary within the range of brightness ratio, the pupil of human eyes will zoom in or out with the brightness ratio, leading to easy fatigue of the eyes.
As illustrated in FIG. 2, the LCD TV curves give a sense of poor image contrast, in addition to showing overload of human eyes after long-lasting TV enjoyment. This is because the pupil cannot provide real-time zoom in/out and timely adjustment. In the event of higher frequency of brightness and darkness, the human eyes cannot duly adjust the light quantity, thus leading to a sense of poor image contrast. For example, when two vehicles pass each other at night, the pupil will automatically zoom out due to high brightness of opposite lamps. After that, there will be an immediate sense of poor vision as the pupil is still in a zoom-out state. Moreover, normal vision can be restored after a period of time due to delayed response of the pupil to sharp changes in brightness.
Furthermore, the strength of ambient light has influence upon the comfort of the audience, especially for enjoying opera (e.g. Cat) that allows reduction in the brightness to create a suitable environment and better visual effect. With the decline of brightness of indoor light, the pupil will zoom in. If the brightness of the LCD TV is not properly reduced, the higher brightness of images will dazzle. So, the brightness of TV images must be properly regulated with the variation of ambient light for an optimum visual effect.
Thus, to overcome the aforementioned problems of the prior art, it would be an advancement in the art to provide an improved structure that can significantly improve the efficacy.
To this end, the inventor has provided the present invention of practicability after deliberate design and evaluation based on years of experience in the production, development and design of related products.